1. Field of the Invention
The present invention relates to an assembly for supporting a magnetic head or a magnetic head slider to float relative to a magnetic disk such as a hard disk and particularly, to an in-line type magnetic head support assembly in which a load beam or arm extends in a direction tangentially of the magnetic disk.
2. Description of the Related Art
In a magnetic disk data storage apparatus, a magnetic head slider is adapted to pitch and roll with dynamic displacement of a magnetic disk so as to accurately read data. A conventional magnetic head support assembly is disclosed, for example, in Japanese laid-open patent publication No. 70977/89. Referring specifically to FIG. 10, the prior art support assembly generally comprises a substantially triangular load arm 2 extending in a direction tangentially of a magnetic disk 4, a magnetic head slider 6 adapted to support a magnetic head (not shown), and an elongated gimbal spring 8 having one end secured to the lower surface of the load arm 2, and the other end secured to the upper surface of the magnetic head slider 6. The load arm 2 includes a flat spring portion 2a, and a rib portion 2b extending from the spring portion 2a and adapted to increase the rigidity of the load arm. The gimbal 8 has a semispherical projection or pivot (not shown), and the load arm 2 has a contact point 2c at its proximal end to contact with the pivot of the gimbal 8. The magnetic head slider 6 is adapted to pitch and roll with movement of the magnetic disk 4 under the influence of the gimbal 8. When the magnetic disk 4 is rotated in a direction as indicated by the arrow A, the magnetic head slider 6 is moved in directions as indicated by the arrow B. As the magnetic disk 4 rotates, air enters between the magnetic disk 4 and the magnetic head slider 6 to form an air spring. To this end, a given load or force is applied from the load arm 2 through the pivot to the magnetic head slider 6 to appropriately float or position the magnetic head slider 6 relative to the magnetic disk 4. In FIG. 10, X and Y indicate circumferential and radial directions of the magnetic disk 4, respectively. Z indicates a direction in which the magnetic head slider 6 is urged toward the magnetic disk 4.
When the magnetic head slider 6 is accelerated in a direction inwardly of the magnetic disk 4 (the arrow B), the resulting inertial force causes application of a force to the contact point 2c of the load arm 2 in "+Y" direction. This results in deformation of the load arm. As shown in FIG. 11, two resonance peaks P1 and P2 appear at a frequency of less than 5 KHz. At the peak P1 or in a primary mode of vibration, the load arm 2 is twisted in "-.theta.X" direction and bent in "+Y" direction as shown by a solid line in FIG. 12A. As a result, the magnetic head slider 6 is moved in "+Y" direction. At the peak P2 or in a secondary mode of vibration, the load arm 2 is twisted in "-.theta.X" direction and bent in "-Y" direction as shown by a solid line in FIG. 12B. As a result, the magnetic head slider 6 is moved in "-Y" direction.
In such a conventional magnetic head support assembly, the rib portion 2b of the load arm 2 has a shear center C (Z&lt;0) above the nominal plane (Z=0) of the load arm throughout its length. If a force F is applied to the contact point 2c, then the load arm 2 is always deformed or twisted in "+.theta.X" direction as shown in FIG. 13A. Also, the spring portion 2a of the load arm is deformed in a manner as shown in FIG. 13B. Referring to FIG. 13C, if a force F is applied to a boundary between the spring portion 2a and the rib portion 2b, the load arm may be deformed in either "+.theta.X" direction or "-.theta.X" direction depending on conditions. However, while the spring portion 2b is bent to exert a load, for example, if 9.5 gf on the magnetic head slider 6, of a force is applied to the contact point 2c of the load arm 2 in "-Y" direction, then the load arm is deforemd in "+.theta.X" direction as shown in FIG. 14.
The flat load arm 2 has high rigidity in a direction in which it is bent, but has low rigidity in which it is twisted. When the load arm 2 is twisted and bent in a dynamic mode of vibration as shown in FIGS. 12A and 12B, resonance peaks appear at a relatively low frequency as shown in FIG. 11. This deteriorates positioning of the magnetic head slider relative to the magnetic disk.